Magnetic flowmeters (or mag meters) measure flow by Faraday induction, an electromagnetic effect. The magnetic flowmeter energizes a coil which generates a magnetic field across a section of a flowtube assembly. The magnetic field induces an electromotive force (EMF) across the flow of conductive process fluid. The resulting potential developed across the conductive fluid is measured using a pair of electrodes that extends into the flowing process fluid. Alternatively, some magnetic flowmeters employ capacitive coupling between the electrodes and the process fluid such that the EMF can be measured without direct contact. In any event, the flow velocity is generally proportional to the induced EMF, and the volumetric flow is proportional to the flow velocity and the cross sectional area of the flowtube.
Magnetic flowmeters are useful in a variety of fluid flow measurement environments. In particular, the flow of water-based fluids, ionic solutions and other conducting fluids can all be measured using magnetic flowmeters. Thus, magnetic flowmeters can be found in water treatment facilities, beverage and hygienic food production, chemical processing, high purity pharmaceutical manufacturing, as well as hazardous and corrosive fluid processing facilities. Magnetic flow meters are often employed in the hydrocarbon fuel industry, which sometimes employ hydraulic fracturing techniques utilizing abrasive and corrosive slurries.
Magnetic flowmeters provide fast, accurate flow measurements in applications where differential pressure-based techniques may be disfavored due to the associated pressure drop across an orifice plate or Venturi tube. In contrast, magnetic flowmeters can be used when it is difficult to introduce a mechanical element into the process fluid flow. Accordingly, a significant proportion of the applications to which magnetic flowmeters are applied involve abrasive and/or corrosive process fluid. When magnetic flowmeters are used in such abrasive applications, the process fluid can wear both the liner and electrodes within the flowtube, which may eventually render the entire magnetic flowmeter inoperable. Historically, the solution to this problem was to replace the flowtube assembly. Providing a magnetic flowmeter flowtube assembly that could be more easily repaired in the field when such wear occurs, for less cost, would advance the art of process fluid flow measurement for such abrasive and/or corrosive applications.